1. Field of the Invention
Methods and apparatuses consistent with the present invention relates to wireless networking, and more particularly, enabling a user to effectively use a wireless network using a contention free channel access service.
2. Description of the Related Art
The IEEE 802.15.4 standard is a low rate wireless personal area network (WPAN) technique, and is considered as a standard for media access control (MAC) and physical (PHY) layers of a wireless center network or a Zigbee network. Implementations of the IEEE 802.15.4 standard should have a low application processing speed, a low cost, and low power consumption, and satisfy timeless characteristics in applications, such as security, control, and monitoring. Therefore, the IEEE 802.15.4 MAC layer adopts a superframe structure and thus introduces a guaranteed time slot (GTS) concept suitable for low power consumption, and real-time or timeless applications.
The size of a superframe depends on an superframe order (SO). The increasing rate of the SO to the time slot is 2. One time slot is divided into backoff boundaries each having a 20 symbol size. For example, when the SO is 0, one time slot is divided into three backoff boundaries. When the SO is 1, one time slot is divided into six backoff boundaries.
FIG. 1 is a diagram illustrating the structure of a general superframe.
As shown in FIG. 1, one superframe is divided into sixteen time slots, devices are allocated with GTSs in the units of time slots. The device exclusively uses the allocated time slot. However, when the allocated time slot is not used for a period that is determined by a standard, the allocation of the time slot is canceled. In addition, since the number of time slots in the superframe is limited to 16, a maximum of seven devices can be allocated with the GTSs. In this case, the GTS is allocated through a beacon. Therefore, when the GTS increases, a beacon frame also increases.
It takes a large amount of time to allocate the GTSs to the devices and to provide services to the devices. When the bandwidth of one time slot is larger than 250 kbps, one device uses a maximum bandwidth of 250 kbps, which causes the unnecessary use of the bandwidth.
Korean Unexamined Patent Publication No. 2002-016733 discloses an access terminal including: a unit that determines a bandwidth in a band to be allocated to a wireless communication terminal and allocates a uniform band at a predetermined bandwidth to the wireless communication terminal; and a unit that receives a transfer rate from a wireless communication terminal that wants to transmit or receive in a contention free period in which the terminal can transmit or receive data in real time, among the wireless communication terminals that are allocated with the uniform band, and adjusts the ratio of the contention free period to the allocated bandwidth according to the received transfer rate. However, Korean Unexamined Patent Publication No. 2002-016733 does not disclose a technique for a contention free channel access service.